6 . 
, 
and bacterial contamination of the "disarmed" host-vector on plates, in liquid 
I' 
culture, during long-term storage and recovery of "disarmed" strains, during shipment 
i 
from one lab to another, all could result in the transfer of the foreign genes 
; to wild type _E. c ol i . The mechanisms will be contaminant plasmid recombination 
l 
or mobilization, contaminant phage recombination, and generalized and specialized 
transduction (possibly by unidentified phages to which the crippled host could 
! not be made resistant, even if it is resistant to some known phages) . The converse 
. 
| situation in which the "disarmed" host- vectors become contaminants of wild- type 
i 
cultures grown by people doing everyday E. coJ_i_ biology down the hall, offers the 
same possibilities of "disarmed" survival and genetic exchange, followed by the 
certainty of entry into the world at large, as such cultures are customarily 
discarded into open sinks. 
Though any of these many possibilities on a given day may be remote, 
their collective -weight over many years and many experiments seems substantial. 
Any of them will have the same result, that. particular foreign genes will end up 
after awhile in the gene pool of wild-type _E. col i , the bacterium indigenous to us. 
With all this (and subsequent ideas on physical containment) in mind, we 
strongly push support for an ecologically appropriate procaryotic host-vector 
system and the abandonment of E, cgU as a host in inter-species recombinant DMA 
experiments. To insure that this transition be mode, the following steps seem 
[ 357 ] 
